That depends on what you're trying to do. You'll have to be more specific if you want a more specific answer. One way that I often make my elements interactive is by adding classes to elements when certain actions are triggered such as hovering or clicking. Then I use jQuery to add that class usually with a transition defined that lets css handle the animation. You could also use pure Javascript/jQuery to handle the action and the animation, but I believe that is more expensive in regards to processing power. I could be wrong on that last part.
